Response of rhizospheric and endophytic bacterial communities of white mustard (Sinapis alba) to bioaugmentation of soil with the Pseudomonas sp. H15 strain.

A factor that may significantly increase the efficacy of phytoextraction is soil bioaugmentation with specific bacteria, which can alter the composition of rhizospheric and endophytic bacterial communities. The aim of this study was to compare the effect of soil treatment with living (bioaugmentation) and dead (control) cells of the plant growth-promoting metal-resistant endophytic strain Pseudomonas sp. H15 on the bacterial community composition in the rhizo- and endo-sphere of white mustard during enhanced phytoextraction. The bacterial communities in the rhizosphere were dominated (51.7-68.2%) by Proteobacteria, regardless of the soil treatment or sampling point. A temporary increase in the number of sequences belonging to Gammaproteobacteria (up to 37.3%) was only observed 24 h after the soil treatment with living Pseudomonas sp. H15 cells, whereas for the remaining samples, the relative abundance of this class did not exceed 7.1%. The relative abundance of Proteobacteria in the endosphere of the roots, stems, and leaves of white mustard was higher in the control than in bioaugmented plants. The most pronounced dominance of the Gammaproteobacteria sequences was observed in the stems and leaves of the control plants at the first sampling point, which strongly indicates the ability of the plants to rapidly uptake DNA from soil and translocate it to the aboveground parts of the plants. Additionally, the bioaugmentation of the soil caused a diverse shift in the bacterial communities in the rhizo- and endo-sphere of white mustard compared to control. The most distinct differences, which were dependent on the treatment, were observed in the endosphere of plants at the beginning of the experiment and decreased over time. These results indicate that the rhizo- and endo-biome of white mustard reacts to soil bioaugmentation and may influence the efficiency of bacterial-assisted phytoextraction.